Remember when the Flopsy Bunnies ate so much of Mr. McGregor’s lettuce that they fell into a deep sleep?  Mr. McGregor was able to pick them right up, put them in a gunny sack and take them home, where Mrs. McGregor vowed to cut off their heads, skin them, and use them to line her coat.

“It is said that eating too much lettuce is soporific,” Beatrix Potter wrote.

I used to think that Potter’s sleep-inducing lettuce  was a plot device, but the milky sap released by cut salad greens is indeed known to calm the nervous system, and to possess a mildly soporific, sometimes euphoric effect. Lettuce is actually named for this sap.  Lactuca, the genus name for both wild and domestic lettuces, is rooted in the Latin lact-, milk, and though our garden varieties were bred by modern agriculturalists to have less of this bitter  substance, plenty of it is still released when we cut into the base of most lettuce heads.   Lettuce sap contains the chemical Lactucarium, a non-narcotic sedative and analgesic, structurally similar to opium, but not nearly as strong.

In ancient Greece, guests were served lettuce soup at the end of a meal to help usher them into dreamland.  Turning this notion of hospitality on its head, the Roman Emperor Domitian was known to torture his guests, who were forbidden to fall asleep in his presence, by serving them heaps of lettuce at the beginning of state dinners (Domitian was assassinated in the year 96–“perhaps justly,” writes Jack Staub in 75 Exciting Vegetables).  And of course throughout Europe salads are still traditionally served at the end of a meal, an homage to lettuce’s sedative properties.

There have been modern scientific studies concluding  that the sleep-inducing qualities of lettuce is simply superstition, but I am somewhat more inclined to believe centuries of cross-cultural medicinal usage above a sterile lab result.

(A Beatrix Potter aside:  I am a fan.  I have heard her dismissed as “Too Cutesie,” which is a terrible midsreading.  Yes, those bunnies are pretty darn adorable, but no cuter than a real passel of sleeping baby rabbits.  Potter’s animals are perfectly wild beneath their ill-fitting clothes, and her reading of the human-wild relationship is wry, biting, and clear-sighted:  “Don’t go into Mr. McGregor’s garden.  Your father had an accident there.  He was put into a pie by Mrs. McGregor.”)